(1) Field of the Invention:
The present invention relates to a heating element having a long durable life and a temperature adjusting performance.
(2) Description of the Prior Art:
There have been known Ni-Cr wire, thermistor, silicon carbide heating elements and the like as a heating element which generates heat by the Joule's heat due to the flowing of electric current.
However, metal wires, such as Ni-Cr wire and the like, generally have low volume resistivity, and it is ordinarily necessary that the metal wires are used in the form of a thin wire in order to obtain a given resistance value, and metal wires have the drawbacks of burn out, short circuit and the like, while, the thermistor has generally a negative temperature coefficient of electric resistance, and therefore when more than a certain value of electric power is applied to a thermistor, electric current is locally concentrated to cause local heating of the thermistor, and when the electric current is excessively large, the thermistor breaks. Therefore, only a bead-shaped thermistor may practically be used, and only very small electric power can be applied to the thermistor.
A heating element using ceramics, such as silicon carbide or the like, is apt to be oxidized at the joint portion of the heating element with the metal terminal due to high temperature. Therefore, only rod-shaped ceramic heating elements having long terminals arranged at both ends of their heat-generating portion have hitherto been used as a ceramic heating element. Accordingly, ceramic heating elements have the drawbacks that a large amount of energy is lost due to the liberation of heat, and the heating element itself is apt to break.